<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <script src="js/vue.js"></script>
</head>
<body>
<div id="app">
  下拉框：
  <select v-model="selected">
    <option disabled value="">请选择</option>
    <option>A</option>
    <option>B</option>
    <option>C</option>
  </select>
  <span>选中的值: {{ selected }}</span>
</div>
</script>
<script>
  var vm = new Vue({
    el: '#app',
    data: {
      selected: ''
    }
  });
</script>

</body>
</html>